Conventional shearing tools take many forms, but usually they employ two overlapping blades arranged in scissor-like fashion or two opposed blades arranged in pincer fashion. Another variation comprises a single blade opposed by an anvil. In all cases the blades, together with their integral handles, are pivoted together and operate as simple levers. The shearing forces that can be developed along the cutting edges of the blades are a function of the length ratio of the handle to the blade portion of each pivoting member. When dealing with objects which are difficult to cut, such as wire cable or other products of metallic or hard substance, conventional shearing tools are inadequate. In order to produce the required shearing forces, the handle-to-blade ratio is increased, which results in a limited cutting blade opening or an awkward handle size which is difficult to operate. Conventional wire cutters, for example, have large handle-to-blade ratios, but are limited to cutting very small wire. When conventional shears are overloaded, the blades tend to spring apart and become permanently deformed, so that they are rendered useless.
Power shearing tools have been developed which employ a cutting blade driven in a straight line by hydraulic means or the like toward a stationary anvil for cutting large or hard objects. However, one disadvantage in this approach is that all of the cutting is done from one side of the work to be cut, thereby severely limiting the effective cutting capacity of the tool for a given amount of power function. In general, power cutters are awkward and difficult to operate. These and other difficulties experienced with the prior art devices have been obviated by the present invention.
It is, therefore, an outstanding object of the invention to provide a shearing tool for hard-to-cut objects which utilizes a fixed cutting edge and a movable cutting edge which is driven towards the fixed cutting edge in a straight line within a shear plane, thereby cutting the object from both sides.
Another object of this invention is the provision of a shearing tool in which the fixed cutting edge is part of a tubular shear member and the movable cutting edge is part of a second shear member, slidably guided within the first tubular shear member to accurately position the cutting edges with respect to each other.
A further object of the present invention is the provision of a shearing tool in which the shear plane bisects the tubular portion of the second shear member, thereby eliminating a binding moment arm.
It is another object of the instant invention to provide a shearing tool in which the first and second shear members have opposed flat surfaces within the shear plane, the first and second cutting edges being formed in the respective first and second flat surfaces to enable the cutting edges to pass each other within the shear plane.
A still further object of the invention is the provision of a shearing tool in which at least the movable second cutting edge is formed by a slot in the second shear which cuts through the flat surface in the second shear member for receiving and holding the work to be cut.
It is a further object of the invention to provide a shearing tool in which the first and second cutting edges diverge within the shear plane toward the bottom of the slot in the second shear member to trap the workpiece in the slot as it is being cut.
It is a still further object of the invention to provide a shearing tool in which the two sides forming each cutting edge are at an acute angle to minimize twisting of the workpiece during shearing.
It is a futher object of the invention to provide a shearing tool in which the driving force for the second or movable cutting edge is hydraulic to provide the necessary power for cutting hard or difficult to cut objects.
It is a further object of the invention to provide a shearing tool in which the cutting elements are mounted in a hydraulically-actuated hand tool which is both simple to use and provides adequate power for cutting difficult to cut objects.
Another object of the invention is the provision of a two-part shearing arrangement in which one part is supported in the other to eliminate the tendancy of the parts to spring apart under the cutting load.